The present invention relates to a zoom lens system and optical apparatus using the same, and more particularly those suitable for video cameras, digital cameras, and cameras using a film.
Along with the recent advance of high performance and miniaturization of cameras (or optical apparatuses), such as video, digital, and electronic still cameras using a charged-coupled device (CCD), and film cameras using a film, an optical system for use with them has been required to meet both high optical performance and miniaturization.
Among a lens system used for an optical apparatus, such as video and digital still cameras, a four-unit zoom lens includes four lens units of positive, negative, positive and positive refractive powers, more specifically, it includes, in order from the object side, a first lens unit of positive refractive power that is fixed during zooming and focusing, a second lens unit of negative refractive power that moves along the optical axis and exhibits a zooming operation, a third lens unit of positive refractive power that is fixed during zooming and focusing, and a fourth lens unit of positive refractive power that moves during zooming and focusing. This four-unit zoom lens exhibits the high optical performance by composing the first lens unit of a cemented lens of a concave lens (or negative lens) and a convex lens (or a positive lens), the second lens unit of two concave lenses and a convex lens, the third lens with one or two convex lenses and a concave lens.
For example, U.S. Pat. Nos. 5,963,378 and 6,166,864 each disclose a zoom lens including, in order from the object side, a fixed first lens unit of positive refractive power, a zooming second lens unit of negative refractive power, a fixed condenser third lens unit of positive refractive power, and a fourth lens unit of positive refractive power that moves along an optical axis to maintain a position of an image plane.
Japanese Laid-Open Patent Applications Nos. Sho 62-206516, Sho 62-24213, Sho 63-247316, and Sho 63-247316, U.S. Pat. No. 5,189,558 disclose another type of four-unit zoom lens including, in order from the object side, a first unit of positive refractive power, a second unit of negative refractive power, a third unit of positive refractive power, and a fourth unit of positive refractive power, wherein the second unit moves and zooms, and the fourth unit corrects fluctuations of the image plane along with the zooming and conducts focusing.
Characteristically, this rear focus type of four-unit zoom lens may easily obtain the predetermined zoom range and easily miniaturize the entire lens system.
On the other hand, various vibration resistant optical systems that serve to prevent blurs in a shot image have been conventionally proposed.
For example, Japanese Laid-Open Patent Application No. Hei 7-128619 discloses a four-unit zooming optical system including four lens units of positive, negative, positive and positive refractive powers, wherein the third lens unit comprises two lens units of positive and negative refractive powers, which lens unit of positive refractive power is made vibratory for vibration resistant purposes.
U.S. Pat. No. 5,585,966 discloses a four-unit zooming optical system including four lens units of positive, negative, positive and positive refractive powers, wherein third lens unit is vibrated for vibration resistant purposes.
Characteristically, these lens units do not require a specific optical member such as a prism, to prevent vibrations, and facilitates the vibration resistance.
Along with the recent advance of high pixel density of image-taking devices, such as digital and video cameras, and miniaturization of optical apparatuses, a smaller and higher performance lens system has been required as a shooting lens for use with them.
In addition, the video camera has been required to record static images with high image quality and to use a high performance and compact lens system.
In general, the enhanced refractive power in each lens unit in the zoom lens would result in a higher zoom range and a shorter lens span because each lens unit moves by a shorter distance to obtain the predetermined zoom range.
However, the simply enhanced refractive power in each lens unit would make stricter the manufacturing precision; for example, the shooting performance remarkably deteriorates due to a relative axial shift among lenses in the third lens unit in the above four-unit zoom lens of positive, negative, positive and positive refractive powers.
On the other hand, the rear focus type zoom lens has been required to have smaller aberrational fluctuations during focusing and during high-range zooming.
Moreover, smaller defocus aberrations are required, when vibrations are prevented, in the optical system that prevents vibrations by decentering part of lenses in a shooting system in a direction perpendicular to the optical axis in order to correct blurred images caused when the lens system vibrates.
Accordingly, it is a primary but exemplified object of the present invention to provide a zoom lens system and an optical apparatus using the same, that are suitable for a shooting system using a photoelectric conversion element such as CCD, compact, and superior in optical performance.
In order to achieve the above object, a zoom lens system of one aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power that doesn""t move along an optical axis for zooming, a second lens unit of negative refractive power that moves along the optical axis for zooming, a third lens unit of positive refractive power that doesn""t move along the optical axis for zooming, the third lens unit including, in order from the object side, a first lens subunit of positive refractive power consisting of one or two positive lens element facing to the object side a convex surface of refractive power that is stronger at the object side than an image side, and a second lens subunit including a cemented lens coupling a concave surface of a negative lens element of refractive power that is stronger at the image side than at the object side, with a convex surface of a positive lens element of refractive power that is stronger at the object side than at the image side, and a fourth lens unit of positive refractive power. The zoom lens system prevents the deterioration of the optical performance, when vibrations are prevented and the third lens unit moves in the direction perpendicular to the optical axis. In addition, the cemented lens in the second lens subunit prevents the performance deterioration caused by the relative axial shift in the third lens unit. This configuration in the third lens unit may make the principal point relatively closer to the second lens unit, shorten a distance from the third lens unit to the image plane, and facilitate the miniaturization of the lens span. Moreover, the lens barrel structure may be made simple and strong to the static pressure by the first lens unit not moved for zooming.
A zoom lens system of another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power that moves along the optical axis for zooming, a third lens unit of positive refractive power including, in order from the object side, a first lens subunit of positive refractive power consisting of one or two positive lens element facing to the object side a convex surface of refractive power that is stronger at the object side than an image side, and a second lens subunit including a cemented lens coupling a concave surface of a negative lens element of refractive power that is stronger at the image side than at the object side, with a convex surface of a positive lens element of refractive power that is stronger at the object side than at the image side, and a fourth lens unit of positive refractive power, wherein a condition 0.09 less than Dab/f3 less than 0.35 is satisfied where Dab is a separation between the first lens subunit and the second lens subunit, and f3 is a focal length of the third lens unit. This zoom lens system prevents the deterioration of the optical performance, when vibrations are prevented and the third lens unit moves in the direction perpendicular to the optical axis. In addition, the cemented lens in the second lens subunit prevents the performance deterioration caused by the relative axial shift in the third lens unit. Moreover, this configuration in the third lens unit may make the principal point relatively closer to the second lens unit, shorten a distance from the third lens unit to the image plane, and facilitate the miniaturization of the lens span.
A zoom lens system of still another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power that moves along the optical axis for zooming, a third lens unit of positive refractive power including, in order from the object side, a first lens subunit of positive refractive power consisting of one or two positive lens element facing to the object side a convex surface of refractive power that is stronger at the object side than an image side, and a second lens subunit including a cemented lens coupling a concave surface of a negative lens element of refractive power stronger at the image side, with a convex surface of a positive lens element of refractive power stronger at the object side, and a fourth lens unit of positive refractive power, wherein a condition 1.67 less than 3G1n less than 1.89 is satisfied where 3G1 is one of positive lens element with an aspherical surface among the first lens subunit, and 3G1n is a refractive index of a material of the positive lens element assigned to 3G1. The zoom lens system prevents the deterioration of the optical performance, when vibrations are prevented and the third lens unit moves in the direction perpendicular to the optical axis. This configuration in the third lens unit may make the principal point relatively closer to the second lens unit, shorten a distance from the third lens unit to the image plane, and facilitate the miniaturization of the lens span.
A zoom lens system of still another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power that moves along the optical axis for zooming, the second lens unit including, in order from the object side, a first negative lens element, a second negative lens element, a third positive lens element, and fourth negative lens element, a third lens unit of positive refractive power, and a fourth lens unit of positive refractive power, wherein conditions 0.81 less than 2G1f/f2 less than 1.25, 20.5 less than 2Glxcexd less than 37.5, and 0.21 less than 2G1f/2G2f less than 0.81 are satisfied where 2G1f is a focal length of the first negative lens element, 2G2f is a focal length of the second negative lens element, f2 is a focal length of the second lens unit, 2Glxcexd is Abbe number of a material of the first negative lens element. In this zoom lens system, the third lens unit may include, in order from the object side, a first lens subunit of positive refractive power consisting of one or two positive lens element facing to the object side a convex surface of refractive power that is stronger at the object side than an image side, and a second lens subunit including a cemented lens coupling a concave surface of a negative lens element of refractive power that is stronger at the image side than at the object side, and a convex surface of a positive lens element of refractive power that is stronger at the object side than at the image side. According to this zoom lens system, the configuration in the second lens unit reduces aberrational fluctuations along with zooming and maintains the high optical performance throughout the entire zoom range.
Any one of the above zoom lens systems preferably satisfies a condition 0.51 less than f3/f4 less than 1.25 where f3 and f4 are focal lengths of the third and fourth lens units, respectively. The image is preferably displaced by moving the third lens unit so as to have a component of a direction perpendicular to an optical axis. The fourth lens unit preferably moves along the optical axis for zooming. The zoom lens system is preferably an optical system for forming images on a photoelectric conversion element.
Any one of the above zoom lens systems preferably satisfies a condition 0.34 less than (3G3R2+3G3R1)/(3G3R2xe2x88x923G3R1) less than 1.34 where 3G3R1 and 3G3R2, respectively, are paraxial radiuses of curvature of surfaces at the object and image sides of the positive lens element that constitutes the cemented lens of the second lens subunit. A condition 0.09 less than Dab/f3 less than 0.35 is preferably satisfied where Dab is a separation between the first lens subunit and the second lens subunit, and f3 is a focal length of the third lens unit. A condition xe2x88x920.25 less than 3af/3bf less than 0.35 is preferably satisfied where 3af and 3bf are focal lengths of the first and second lens units, respectively.
A zoom lens system of still another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power that moves along the optical axis for zooming, a third lens unit of positive refractive power including, in order from the object side, a first lens subunit of positive refractive power consisting of one or two positive lens element facing to the object side a convex surface of refractive power, and a second lens subunit including a cemented lens coupling with a negative lens element facing a concave surface thereof to the image side, with a positive lens element facing a convex surface thereof to the object side, and a fourth lens unit of positive refractive power, wherein conditions 0.09 less than Dab/f3 less than 0.35, 0.51 less than f3/f4 less than 1.25, 0.34 less than (3G3R2+3G3R1)/(3G3R2xe2x88x923G3R1) less than 1.34, and xe2x88x920.25 less than 3af/3bf less than 0.35 are satisfied where Dab is a separation between the first lens subunit and the object side of the second lens subunit, fi is a focal length of the i-th lens unit, 3af and 3bf are focal lengths of the first and second lens subunits, respectively, and 3G3R1 and 3G3R2, respectively, are paraxial radiuses of curvature on surfaces at the object and image sides of the positive lens element that constitutes the cemented lens of the second lens subunit. This zoom lens system may also achieve operations similar to the above zoom lens systems.
This zoom lens system preferably satisfies a condition 1.67 less than 3G1n less than 1.89 where 3G1 is preferably one of positive lens element with an aspherical surface facing a concave surface to the object side among the first lens subunit, and 3G1n is a refractive index of a material of the positive lens element assigned to 3G1. The second lens unit in this zoom lens system preferably includes, in order from the object side, a first negative lens element, a second negative lens element, a third positive lens element, and fourth negative lens element, and wherein conditions 0.81 less than 2G1f/f2 less than 1.25, 20.5 less than 2Glxcexd less than 37.5, and 0.21 less than 2G1f/2G2f less than 0.81 are preferably satisfied where 2G1f is a focal length of the first negative lens element in the second lens unit, 2G2f is a focal length of the second negative lens element in the second lens unit, f2 is a focal length of the second lens unit, 2Glxcexd is Abbe number of a material of the first negative lens element in the second lens unit. In this zoom lens system, the fourth lens unit preferably moves along the optical axis for zooming. In addition, in this zoom lens system, the image is preferably displaced by moving the third lens unit so as to have a component of a direction perpendicular to an optical axis. In this zoom lens system, the system is preferably an optical system for forming an image on a photoelectric conversion element.
A zoom lens system of still another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power that doesn""t move along an optical axis for zooming, a second lens unit of negative refractive power that moves along the optical axis for zooming, a third lens unit of positive refractive power including, in order from the object side, a first lens subunit of positive refractive power having a positive lens element facing a convex surface thereof to the object side, a stop, and a second lens subunit including a cemented lens coupling a negative lens element facing a concave surface thereof to the image side, with a positive lens element facing a convex surface thereof to the object side, and a fourth lens unit of positive refractive power.
A zoom lens system of still another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power including, in order from the object side, a first lens subunit of positive refractive power having a positive lens element facing a convex surface thereof to the object side, a stop, and a second lens subunit including a cemented lens coupling a negative lens element facing a concave surface thereof to the image side, with a positive lens element facing a convex surface thereof to the object side, and a fourth lens unit of positive refractive power, wherein a condition 0.08 less than Dab/f3 less than 0.64 is satisfied where Dab is a separation between the first and second lens subunits, and f3 is a focal length of the third lens unit.
A zoom lens system of still another aspect of the present invention includes, in order from an object side, a first lens unit of positive refractive power, a second lens unit of negative refractive power, a third lens unit of positive refractive power including, in order from the object side, a first positive lens element having an aspherical surface facing a convex surface thereof to the object side, a stop, and a negative lens element facing a concave surface thereof to the image side, and a second positive lens element facing a convex surface thereof to the object side, and a fourth lens unit of positive refractive power, wherein a condition 1.67 less than 3G1n less than 1.89 is satisfied where 3G1n is a refractive index of a material of the first positive lens element in the third lens unit.
The aforementioned zoom lens systems may make smaller a separation between the second and third lens units that becomes the shortest at the longest focal length end in the entire system (i.e., the telephoto end) than the four-unit zoom lens in which the stop is located just in front of the third lens unit, thus improving the zoom efficiency and making small the lens span. The stop located between the first and second lens units may prevent the deterioration in the optical performance caused by the relative axial shift between the first and second lens units in the third lens unit. This configuration in the third lens unit may make the principal point relatively closer to the second lens unit, shorten a distance from the third lens unit to the image plane, and facilitate the miniaturization of the lens span.
Any one of the above three zoom lens systems preferably satisfies a condition 0.71 less than f3/f4 less than 1.41 where f3 and f4 are focal lengths of the third and fourth lens units, respectively. The second lens unit preferably has an aspherical surface. The fourth lens unit preferably moves along the optical axis for zooming. A condition 0.64 less than (3G3R2+3G3R1)/(3G3R2-3G3R1) less than 1.64 is preferably satisfied where 3G3R1 and 3G3R2, respectively, are paraxial radiuses of curvature on surfaces at the object and image sides of the positive lens element that constitutes the cemented lens of the second lens subunit. In this zoom lens system, the system is preferably an optical system for forming an image on a photoelectric conversion element.
Any one of the above three zoom lens systems also preferably satisfies a condition xe2x88x920.81 less than 3af/3bf less than 0.35 where 3af and 3bf are focal lengths of the first and second lens units, respectively. Any one of the above three zoom lens systems also preferably satisfies a condition 0.01 less than (D12w+D23t)/BD2 less than 0.84 where D12w is a separation between the first and second lens units when said zoom lens system has the shortest focal length, D23t is a separation between said second and third lens units when said zoom lens system has the shortest focal length, and BD2 is a separation between a surface closest to the object side and a surface closest to the image side in said second lens unit. Any one of the above three zoom lens systems also preferably satisfies a condition 0.08 less than Dab/f3 less than 0.64 where Dab is a separation between the first positive lens element and the second negative lens element, and f3 is a focal length of the third lens unit.
An optical apparatus of still another aspect of the present invention includes the aforementioned zoom lens system and a photoelectric conversion element for receiving an image formed by the zoom lens system.
Other objects and further features of the present invention will become readily apparent from the following description of preferred embodiments with reference to accompanying drawings.